Abstract
The luminescence efficiency of lanthanide-doped upconversion nanoparticles is of particular importance for their embodiment in biophotonic and photonic applications. Here, we show that the upconversion luminescence of typically used NaYF4:Yb3+30%/Tm3+0.5% nanoparticles can be enhanced by ~240 times through a hierarchical active core/active shell/inert shell (NaYF4:Yb3+30%/Tm3+0.5%)/NaYbF4/NaYF4 design, which involves the use of directed energy migration in the second active shell layer. The resulting active core/active shell/inert shell nanoparticles are determined to be about 11 times brighter than that of well-investigated (NaYF4:Yb3+30%/Tm3+0.5%)/NaYF4 active core/inert shell nanoparticles when excited at ~980 nm. The strategy for enhanced upconversion in Yb3+/Tm3+-codoped NaYF4 nanoparticles through directed energy migration might have implications for other types of lanthanide-doped upconversion nanoparticles.
Highlights
Lanthanide-doped upconversion nanoparticles (UCNPs) are able to convert near infrared light (NIR) into shorter wavelength NIR, visible, and ultraviolet (UV) emissions, and have important technological applications ranging from bioimaging, displays, photovoltaics, drug delivery, biosensors, to photodynamic therapy [1,2,3,4,5]
We report on a new design of (NaYF4:Yb3+30%/Tm3+0.5%)/NaYbF4/NaYF4 active core/active shell/inert shell UCNPs
Compared to the size of the core NaYF4: 30%Yb3+, 0.5%Tm3+ nanoparticle, the size increase in the active core/inert shell and the active core/active shell nanoparticles indicates the successful growth of shell layer
Summary
Lanthanide-doped upconversion nanoparticles (UCNPs) are able to convert near infrared light (NIR) into shorter wavelength NIR, visible, and ultraviolet (UV) emissions, and have important technological applications ranging from bioimaging, displays, photovoltaics, drug delivery, biosensors, to photodynamic therapy [1,2,3,4,5]. NaYF4 nanoparticels are of particular interests, because NaYF4 has been shown to be the most efficient host material for UCNPs [7,19], and because they display luminescence in the NIR, blue and UV range, which are useful for bioimaging [20], photoactivation [21], and light-activated therapy [22] Until this point, there has been no report on utilizing the active shell to increase the upconversion luminescence of Yb3+/Tm3+-doped NaYF4 UCNPs. In this work, we report on a new design of (NaYF4:Yb3+30%/Tm3+0.5%)/NaYbF4/NaYF4 active core/active shell/inert shell UCNPs. Unlike previously reported active core/active shell UCNPs with limited amount of Yb3+ concentration (20%) in the active shell, the active shell here incorporates 100% of Yb3+ ions to harvest excitation photon more efficiently. As a result of the use of outmost inert NaYF4 shell to block the pathways to surface quenching cites, all energy migration within the NaYbF4 active shell layer have been directed to sensitize lanthanide ions in the core nanoparticles, yielding efficient UC luminescence about ~240 times higher than that of the typically used NaYF4:Yb3+30%/Tm3+0.5% UCNPs, and about 11 times brighter than that of the well-investigated active core/inert shell (NaYF4:Yb3+30%/Tm3+0.5%)/NaYF4 UCNPs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
